JPH09295459A - Formation of image having improved slip performance by heat - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an image by heat in which the defect of the image is removed in most of the printing conditions. SOLUTION: In a method for forming an image by heat, (1) the outermost layer of recording material is brought into contact with a heat source. The recording material is constituted by containing at least one kind of thermal element which contains essentially a nonsensitizing silver salt and a reducing agent that is in thermal action relation thereto and is used therefor on a supporting body. (2) Heat is applied to the recording material according to an image from the heat source while holding mutual contact through relative movement between the recording material and the heat source. (3) A stage for separating the recording material from the heat source is incorporated. Dynamic friction coefficient during contact between the outermost layer of the recording material and the heat source has the maximum value smaller than 0.3. The outermost layer of the recording material coming into contact with the heat souce may be the outermost layer of the thermal element, a protective layer applied to the thermal element or a layer on the side opposite to the thermal element of the supporting body.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to thermographic materials suitable for thermal development in dynamic contact with a heat source. In particular, it relates to an improvement in the imaging properties due to its surface in contact with a heat source having specific slip properties.

[0002]

BACKGROUND OF THE INVENTION Thermal imaging or thermography is a recording method in which an image is formed by the use of imagewise modulated thermal energy.

An overview of "direct thermal" imaging methods is given, for example, by Kurt I. Jacobson-Ralph E. Jacobson in the book "Imaging Systems", The Focal Press-London.
and New York (1976), Chapter VII "7.1 Thermogr
Direct thermal imaging is related to materials that are substantially non-photosensitive but are heat-sensitive or heat-sensitive. Image-wise applied The heat is sufficient to cause a visible change in the heat-sensitive imaging element.

The majority of "direct" thermographic recording materials are of the chemical type. Upon heating to some conversion temperature, irreversible chemical reactions occur and a colored image is formed.

According to US Pat. No. 3,080,254,
Typical thermosensitive copying papers have a thermoplastic binder such as ethyl cellulose, a water insoluble silver salt such as silver stearate and a suitable organic reducing agent such as 4-methoxy-1 in the heat sensitive layer. -Hydroxy-
Contains dihydronaphthalene. In the thermographic reproduction method or for testing purposes, localized heating of the sheet by temporary contact with a metal test bar heated to a suitable conversion temperature in the range of about 90-150 ° C. is visible in the heat-sensitive layer. Cause a visible change. The initially white or lightly colored layer darkens to a brownish appearance in the heated area. To obtain a more pure color tone, a heterocyclic organic toning agent such as phthalazinone is added to the composition of the heat-sensitive layer. "Front side printing" or "back side" using infrared radiation that is absorbed and converted to heat in contact with the original infrared absorbing image portion as shown in FIGS. 1 and 2 of US Pat. No. 3,080,254. Thermal copy paper is used for printing.

Direct thermal imaging materials based on silver salts show white lines with strong changes in print density. W
O94 / 11199 has attempted to solve the white line problem and has (i) a substantially non-photosensitive organic silver salt on the support, (ii) hot melt particles dispersed in a binder. A recording material comprising a protective layer contained and (iii) a heat-sensitive layer and / or a reducing agent present on the same side as the heat-sensitive layer in another layer is disclosed. It also teaches that the protective layer may further comprise a lubricant or the lubricant may be present on top of the protective layer.

In the course of the work leading up to the present application, the use of a protective layer containing heat-fusible particles with a lubricant or with a lubricant on top of the protective layer disclosed in WO 94/11199 occurs in the transport direction. It has been found to be insufficient to prevent image defects under a wide range of printing conditions.

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide a thermal imaging method in which image defects are eliminated under most printing conditions.

Other objects and advantages of the invention will be apparent from the description below.

[0010]

SUMMARY OF THE INVENTION The above objects include on a support at least one heat-sensitive element comprising (i) a substantially light-insensitive silver salt and a reducing agent therefor in thermal working relationship therewith. Contacting the outermost layer of the recording material with a heat source, and (ii) applying heat from the heat source to the recording material while maintaining mutual contact with relative motion between the recording material and the heat source. And (iii) a thermal imaging method comprising the step of separating the recording material from the heat source, the dynamics during the contact between the outermost layer of the recording material and the heat source. The method is characterized in that the coefficient of friction has a maximum value less than 0.3.

Preferred aspects of the invention are described in the main features and aspects section below.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described by way of example with reference to the accompanying drawings: FIG. 1 shows the strain gauge response (volts) printout as a function of printing time (seconds).
-out) (= print position with 11 blocks each printed with different electrical energy per dot)
Is used to measure the maximum and minimum strain gauge signals (volts) (shown), from which the dynamic coefficient of friction is calculated.

According to the invention, the coefficient of dynamic friction, μ, is defined as follows: μ = (F−R) / L where F is the recording material passing through the heat source at a specified speed. Is the lateral strain applied to the strain gauge connected to the heat source, R is the rotational resistance of the transfer drum, and L is the load applied to the heat source perpendicular to the transfer direction of the recording material].

According to one aspect of the invention, the ratio of the maximum dynamic coefficient of friction to the minimum dynamic coefficient of friction is less than 1.9.

According to another aspect of the invention, the heat source is a thin film thermal head.

Outermost layer in contact with the heat source The outermost layer in contact with the heat source is, in various embodiments of the invention, the outermost layer of the heat-sensitive element, the protective layer applied to the heat-sensitive element or the heat-sensitive element. It may be a layer on the opposite side of the support.

The maximum dynamic coefficient of friction of less than 0.3 between the heat source and the outermost layer in contact with the heat source is WO 94 /
One or more matting agents as described in 11198 and optionally one or more lubricants as described in WO94 / 11198. The melting point below 150 ° C. of at least one of the abovementioned fusible particles or in a binder in which at least one of the lubricants as described in the pending European patent application is a phosphoric acid derivative. Obtained by a person skilled in the art by the combination with a solid lubricant and at least one liquid lubricant.

Protective Layer The outermost layer of the recording material according to the present invention may be a protective layer applied to avoid local deformation of the heat-sensitive element and improve resistance to abrasion.

The protective layer is preferably hydrophobic (solvent soluble)
Alternatively, it comprises a binder which may be hydrophilic (water-soluble). Among the hydrophobic binders, the polycarbonates described in EP-A 614 769 are particularly preferred. However, since the coating can be done from an aqueous composition and mixing of the hydrophilic protective layer with the intermediate subbing layer is avoided by the use of a hydrophobic binder in the intermediate subbing layer, the hydrophilic binder is a protective layer. Is preferably used as.

As described in WO 94/11198, such a protective layer may comprise particulate matter, such as talc particles, optionally protruding from the outermost layer. Other additives, such as colloidal particles, such as colloidal silica, may be added in the protective layer.

Hydrophilic Binder for Outermost Layer According to one aspect of the invention, the outermost layer of the recording material in contact with the heat source may comprise a hydrophilic binder. Suitable hydrophilic binders for the outermost layer in contact with the heat source are, for example, gelatin, polyvinyl alcohol,
Cellulose derivatives or other polysaccharides, hydroxyethyl cellulose, hydroxypropyl cellulose and the like, curable binders are preferred and polyvinyl alcohol is particularly preferred.

Crosslinking Agent for Outermost Layer According to one embodiment of the present invention, the outermost layer of the recording material in contact with the heat source may be crosslinked. The cross-linking is carried out, for example, by using cross-linking agents for protective layers as described in WO 94/11198, for example tetra-alkoxysilanes, polyisocyanates, zirconates, titanates, melamine resins and the like. Tetraalkoxysilanes such as tetramethyl orthosilicate and tetraethyl orthosilicate are preferred.

Matting Agent for Outermost Layer The outermost layer of the recording material in contact with the heat source according to the present invention may comprise a matting agent. Suitable matting agents are described in WO 94/11198 and include, for example, talc particles which may project from the outermost layer.

Lubricant for Outermost Layer The outermost layer of the recording material according to the present invention may comprise at least one lubricant. Examples of suitable lubricating substances are surface-active agents, liquid lubricants, solid lubricants which do not melt during the thermal development of the recording material, solid lubricants which melt during the thermal development of the recording material (heat-meltable) or It is a mixture of them. The lubricant can be applied with or without a polymeric binder. Surface active agents known agents in the art such as carboxylates, sulfonates, aliphatic amines, aliphatic quaternary ammonium salts, polyoxyethylene alkyl ethers, polyethylene glycol fatty acid esters, fluoroalkyl C ₂ - It may be C ₂₀ fatty acids. Examples of liquid lubricants include silicone oils, synthetic oils, saturated hydrocarbons, glycols and phosphoric acid derivatives. Examples of solid lubricants include various higher alcohols such as stearyl alcohol, and fatty acids, phosphoric acid derivatives, fatty acid esters, fatty acid amides, polyolefin-polyether block copolymers,
Included are polysiloxane-polyether copolymers and polytetrafluoroethylene.

The lubricant is preferably selected from the group consisting of silicone derivatives, polyolefins, fatty acid derivatives, fatty alcohol derivatives and phosphoric acid derivatives.

A preferred embodiment is at least one of the lubricants as disclosed in the pending European patent application.
15 of at least one species in a binder wherein the species is a phosphoric acid derivative
The use of solid lubricants having a melting point below 0 ° C. and at least one liquid lubricant. Examples of suitable hot-melt solid non-phosphoric acid derivative lubricants, along with their melting points, are given below.

Melting point [° C.] SL01: Ethylenebisstearamide (141 Ceridust ^™ from Hoichst AG) SL02: myristamide 106 SL03: stearamide 104 SL04: glyceryl monostearate 81 SL05: erucamide ( erucamide 80 SL06: oleamide 73 SL07: glyceryl tristearate 55-73 SL08: Mobilcer ^™ Q (paraffin wax) 67 SL09: glycerine monotallow fatty acid ester (Rilanit ^™ GMS from Henkel AG 55-60) SL10: Sorbitan monostearate (55 SPAN ^TM 60 from ICI PLC) SL11: Sorbitan tristearate (48-53 SPAN ^TM 65 from ICI PLC) SL12: Sorbitan monopalmitate (44-47 SPAN ^TM 40 from ICI PLC) SL13: Monostearic acid POE- (4) SO Tail (TWEEN ^TM 61 from ICI PLC 36-40) suitable phosphate derivatives heat meltable solid lubricant is an example of (PSL) are shown below together with their melting points.

Melting point [° C.] PSL01: Servoxyl ^™ VPAZ 100 33 from Servo Delden BV (mixture of monolauryl and dilauryl phosphate) PSL02: Servoxyl ^™ VPRZ 100 50 (mixture of monocetyl and monostearyl phosphate) from Servo Delden BV PSL03 : Potassium alkyl phosphate (62 Crafol ^™ AP37 from Henkel AG) Examples of suitable non-phosphoric acid derivative liquid lubricants (LL) are given below.

LL01: glyceryl trioleate LL02: sorbitan monooleate (SPAN ^™ 80 from Henkel AG) LL03: sorbitan trioleate (SPAN ^™ 85 from Henkel AG) LL04: Tegoglide ^™ ZG 400 from TEGO-chemie An example of a suitable phosphoric acid derivative liquid lubricant (PLL) is shown below.

PLL01: Ser from Servo Delden BV
voxyl ^TM VPDZ 3 100 {monocalcium phosphate [isotridecyl polyglycol ether (3EO)]} PLL02: Servo Servoxyl TM VPRZ from Delden BV
6 100 {phosphate mono [isotridecyl polyglycol ether (6EO)]} PLL03: Servoxyl ^™ VPFZ from Servo Delden BV
7 100 {phosphate mono [oleyl polyglycol ether (7
EO)]} PLL04: Sermul ^TM EA224 from Servo Delden BV
(= Servoxyl ^™ VPFZ 7100) {Phosphoric acid mono [oleyl polyglycol ether (7EO)]} Thermosensitive element The thermosensitive element according to the invention comprises a substantially non-photosensitive silver salt and a reducing agent therefor in thermal working relationship therewith. It consists of The substantially non-photosensitive silver salt and the reducing agent are in thermal relationship with each other, that is, the reducing agent diffuses the substantially non-photosensitive silver salt particles during the thermal development process to cause reduction of the silver salt. To the extent possible, this element may comprise a layer system in which each component may be dispersed in different layers.

Substantially Light Insensitive Silver Salt Suitable substantially light insensitive silver salts according to the present invention are substantially light insensitive organic silver salts. Suitable substantially non-photosensitive organic silver salts are silver salts of aliphatic carboxylic acids known as fatty acids whose aliphatic carbon chains have at least 12 C atoms, such as silver laurate, silver palmitate, stearin. Acid silver, silver hydroxystearate, silver oleate and silver behenate, with silver behenate being particularly preferred. Such silver salts are also called "silver soaps". Further, silver dodecyl sulfonate described in U.S. Pat. No. 4,504,575 and silver di- (2-ethylhexyl) -sulfosuccinate described in EP-A 227 141, for example, British Patent No. 1,
Modified aliphatic carboxylic acids having a thioether group as described in 111,492, and other organic silver salts as described, for example, in British Patent 1,439,478, such as silver benzoate and silver phthalazinone, Can likewise be used to form a thermally developable silver image. further,
Silver imidazolates and US Pat. No. 4,260,677
The substantially non-photosensitive inorganic or organic silver salt complexes described in US Pat.

The silver image density depends on the coverage of one or more reducing agents and one or more organic silver salts as defined above, and preferably at least when heated above 100 ° C. It must be possible to obtain an optical density of 2.5.

Reducing Agent Suitable reducing agents according to the present invention are organic reducing agents. Suitable organic reducing agents for the reduction of the substantially light-insensitive silver salt are O,
Organic compounds containing at least one active hydrogen atom bonded to N or C, such as aromatic di- and tri-hydroxy compounds, aminophenols, METOL (trade name), p-phenylenediamines, alkoxynaphthols , 4-methoxy-1-naphthol, pyrazolidine-3 described in, for example, U.S. Pat. No. 3,094,417.
-On-type reducing agents such as PHENIDON (trade name),
Pyrazolin-5-ones, indan-1,3-dione derivatives, hydroxytetronic acids, hydroxytetronimides, such as the hydroxylamine derivatives described in US Pat. No. 4,082,901, hydrazine derivatives, and ascorbic acid, for example. Reductones such as
U.S. Pat. Nos. 3,074,809, 3,080,254
See also Nos. 3,094,417 and 3,887,378.

Among the useful aromatic di- and tri-hydroxy compounds having at least two hydroxy groups on the same aromatic nucleus, for example the benzene nucleus, in the ortho- or para-position, hydroquinone and substituted Hydroquinones, catechol, pyrogallol, gallic acid and gallic acid esters are preferred. Polyhydrospiro-bis-indane compounds are particularly useful, in particular they are of the general formula (I):

[0035]

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[Wherein R represents hydrogen or alkyl, for example methyl or ethyl, and each of R ⁵ and R ⁶ (identical or different) is an alkyl group, preferably a methyl group, or a cycloalkyl group, for example cyclohexyl. R ⁷ and R ⁸ (identical or different) each represents an alkyl group, preferably a methyl group or a cycloalkyl group such as a cyclohexyl group, and Z ¹ and Z ² (identical or different) represent Alt or Para
Represents an aromatic ring or ring system which is substituted in the position by at least two hydroxyl groups and optionally further substituted by at least one hydrocarbon group such as an alkyl or aryl group, eg a benzene ring. To do.

In particular, the polyhydroxy-spiro-bis-indane compounds described as photographic tanning agents in US Pat. No. 3,440,049, more particularly 3,3,3 ', 3'.
-Tetramethyl-5,6,5 ', 6'-tetrahydroxy-1,1'-spiro-bis-indane (designated indane I) and 3,3,3', 3'-tetramethyl-4,6 ,
Particular mention is made of 7,4 ', 6', 7'-hexahydroxy-1,1'-spiro-bis-indane (designated indane II). Indan is also known as Hydlinden.

Catechol-type reducing agent, ie 2
Among the reducing agents containing at least one benzene nucleus having 4 hydroxy groups (-OH) in the ortho-position,
The following are preferred: catechol, 3- (3,4-dihydroxyphenyl) propionic acid, 1,2-dihydroxybenzoic acid, gallic acid and its esters, such as methyl gallate, ethyl gallate, propyl gallate. , Tannic acid, and 3,4-dihydroxy-benzoic acid esters. A particularly suitable catechol-type reducing agent described in EP-A 692 733 is a benzene nucleus in which the benzene nucleus is located at the 3,4-position on the nucleus and is bonded to the nucleus by a carbonyl bond at the 1-position of the nucleus. A benzene compound substituted with no more than two hydroxy groups having the specified substituents.

The silver image density depends on the coverage of the reducing agent and the silver salt and should preferably be heated so that an optical density of at least 2.5 is obtained on heating. Preferably at least 0.10 mol of reducing agent is used per mol of silver salt.

Auxiliary Reducing Agents The reducing agents mentioned above, which are regarded as main or main reducing agents, may be used together with so-called auxiliary reducing agents. Such auxiliary reducing agents are, for example, sterically hindered phenols which are reaction partners in the reduction of a substantially non-photosensitive silver salt upon heating, such as silver behenate described in US Pat. No. 4,001,026. , Or bisphenols of the type described in US Pat. No. 3,547,648. The auxiliary reducing agent can be present in the imaging layer or in the polymeric binder layer in thermal working relationship therewith.

Suitable co-reducing agents are of the general formula: Aryl-SO ₂ -NH-arylene-OH, wherein aryl represents a monovalent aromatic group and arylene is preferably -SO ₂ -NH. Represents a divalent aromatic group having an —OH group in the para position to the group.

Sulfonamide phenols according to the general formula defined above are periodic publications Research Disc
losure, February 1979, item 17842, U.S. Pat. Nos. 4,360,581 and 4,782,004, and EP-A 423 891, wherein these reducing agents are essentially organic acids. Are listed for use in photothermographic recording materials which are in close contact with silver salts which are optically insensitive.

Other co-reducing agents that can be used with the primary reducing agents described above are organometallic salts such as US Pat. No. 3,460,
Stannous stearate described in No. 946 and No. 3,547,648.

Film-Forming Binders for Heat-Sensitive Elements Film-forming binders for heat-sensitive elements containing a substantially light-insensitive silver salt are all types of natural, in which the silver salt is homogeneously dispersible, Derived from modified natural or synthetic resins or mixtures of such resins, for example cellulose derivatives such as ethyl cellulose, cellulose esters such as cellulose nitrate, carboxymethyl cellulose, starch ethers, galactomannans, α, β-ethylenically unsaturated compounds. Polymers such as polyvinyl chloride, post-chlorinated polyvinyl chloride, copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and vinyl acetate, polyvinyl acetate and partially hydrolyzed Made from polyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol as a starting material Therefore, only a part of repeating vinyl alcohol units may react with an aldehyde, polyvinyl acetals, preferably polyvinyl butyral, copolymers of acrylonitrile and acrylamide, polyacrylic acid esters, polymethacrylic acid esters, polystyrene. And polyethylene or mixtures thereof.

A particularly suitable polyvinyl butyral containing small amounts of vinyl alcohol units is sold under the trade name BUTVAR B79 of Monsanto USA and gives good adhesion to paper and suitably subbed polyester substrates.

The weight ratio of binder to silver salt is preferably 0.2-.
6 and the recording layer thickness is preferably 5-5.
The range is 0 μm.

The layer containing the silver salt is generally coated on a support in sheet or web form from an organic solvent containing a binder therein, but in the form of a latex from an aqueous medium, eg an aqueous polymer dispersion. It can also be applied in liquid form. For use in latex, the dispersible polymer preferably has some hydrophilic functionality. Polymers having hydrophilic functionality for making aqueous polymer dispersions (latex) are described, for example, in US Pat. No. 5,006,451, which is present as an antistatic agent therein. It functions to form a shielding layer that prevents unwanted diffusion of vanadium oxide.

The above-mentioned binders or mixtures thereof are waxes or "thermal solvents".
s) ”or“ thermosolvents ”, also referred to as“ thermosolvents ”, to improve the kinetics of redox reactions at elevated temperatures.

The term "thermal solvent" in the context of the present invention is used in the recording layer in the solid state at temperatures below 50 ° C. but for heated and / or at least one redox reactant such as a silver salt. 6 in liquid solvent for reducing agent
It means a non-hydrolyzable organic substance which becomes a plasticizer for the recording layer at a temperature above 0 ° C. U.S. Pat. No. 3,347,
Polyethylene glycols having an average molecular weight in the range of 1,500 to 20,000 described in 675 are useful for this purpose. Compounds such as the thermal solvents urea, methylsulfonamide and ethylene carbonate described in U.S. Pat. No. 3,667,959, and Research Di
sclosure, December 1976, (item 15027) pages 26-28
Described as hot solvents in, for example, tetrahydro-thiophene-1,1-dioxide, methyl anisate and 1,1
Further included are compounds such as 0-decanediol.
Still other examples of thermal solvents are U.S. Pat. Nos. 3,438,776 and 4,740,446, published EP-A 0.
119 615 and 0122 512, and DE-A
3 339 810.

Toning agent In order to obtain a relatively high density of pure black tones and a relatively low density of pure gray, the recording layer is preferably a so-called toning agent known from thermography or photothermography, preferably the silver salt and Contains by mixing with a reducing agent.

A suitable toning agent is US Pat. No. 4,082,90.
Phthalimides and phthalazinones within the general formula described in No. 1. U.S. Pat. No. 3,074,809
Reference is also made to the toning agents described in Nos. 3,446,648 and 3,844,797. Other particularly useful toning agents have the general formula:

[0052]

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[Wherein, X represents O or N-alkyl, and R ¹ , R ² , R ³ and R ⁴ (identical or different))
Each is hydrogen, alkyl, for example C1-C20 alkyl, preferably C1-C4 alkyl, cycloalkyl, for example cyclopentyl or cyclohexyl, alkoxy, preferably methoxy or ethoxy, preferably alkylthio having up to 2 carbon atoms. , Hydroxy, a dialkylamino whose alkyl group preferably has up to 2 carbon atoms or halogen, preferably chlorine or bromine, or R ¹ and R ² or R ² and R ³ are fused aromatic rings, For example, a benzene ring, or R ³ and R ⁴ represent a ring member required to complete a fused aromatic or cyclohexane ring] Alternatively, it is a naphthoxazinedione type heterocyclic toning compound. Toning agents within the general formula are described in German Patent 1,439,478 and US Patent 3,951,660.

Toning compounds suitable for use in combination with a polyhydroxybenzene reducing agent are described in US Pat. No. 3,951,
3,4-dihydro-2,4-dioxo-1,3,2H-benzoxazine described in No. 660.

Other Components In addition to the above components, the recording layer contains, for example, free fatty acids, surfactants, antistatic agents, for example, nonionic antistatic agents containing a fluorocarbon group, such as F ₃ C (CF ₂ ) ₆ CONH. (C
H ₂ CH ₂ O) -H, silicone oils such as BAYSILONEOEl
Other additives such as A (trade name of BAYER AG-GERMANY), UV absorbing compounds, white light reflecting and / or UV reflecting pigments, silica, and / or optical brighteners may also be included.

Support The support for the thermal imaging element according to the invention may be transparent, translucent or opaque, for example having a white light-reflecting surface, and is preferably for example paper, polyethylene. Thin flexible carrier made from coating paper,
Or a cellulose ester, such as cellulose triacetate,
It may be a transparent resin film made of polypropylene, polycarbonate or polyester, such as polyethylene terephthalate. For example, there are paper base substrates that may optionally contain a white reflective pigment applied in an interlayer between the recording material and the paper base substrate.

The support may be in the form of a sheet, ribbon or web and optionally subbed on the top to improve adhesion to the coated thermal recording layer. The support is an opaque resin composition,
It may be made of polyethylene terephthalate, for example pigmented and / or opaque with micropores and / or coated with an opaque pigment-binder layer, and may be a so-called synthetic paper or paper-like film, Information regarding such supports can be found in European Patents 194 106 and 234 563 and U.S. Patents 3,994,699, 4,187,113.
Nos. 4,780,402 and 5,059,579. If a transparent base is used, it may be colorless or coloured, for example having a blue color.

Antistatic Layer In a preferred embodiment of the recording material of the invention, an antistatic layer is applied to the outermost layer which does not come into contact with the heat source during the thermal imaging process. An antistatic layer suitable therefor is EP-A 4
40 957.

Coating The coating of any of the layers of the recording material of the present invention is described in Modern Coating and Drying Technology, (19) edited by Edward D. Cohen and Edgar B. Gutoff, for example.
92) VCH Publishers Inc. 220 East 23rd Street, Suit
It can be done by a coating technique such as e 909 New York, NY 10010, USA.

Processing Structure "Handbook of Im" edited by Arthur S. Diamond
aging Materials ", -Diamond Reserch Corporation-V
entura, Calfornia, printed by Marcel Dekker, Inc.
270 Madison Avenue, New York, New York 10016 (199
1), p. 498-502, in thermal printing the image signal is converted into electrical pulses and then selectively transferred through a drive circuit to a thermal print head. Thermal printing heads consist of microscope thermal resistor elements that convert electrical energy into heat by the Joule effect. The electric pulse itself thus converted into a heat signal is heat-transferred to the surface of the hot paper, where a chemical reaction that causes color development occurs. In order to ensure good heat transfer, the operating temperature of a typical thermal print head is in the range of 300-400 ° C. and the heating time per picture element (pixel) is 50 ms or less, The pressure contact between the thermal printing head and the recording material is, for example, 100-500 g / cm ² .

In a special embodiment of the method according to the invention, the direct thermal image-wise heating of the recording material is carried out by Joule effect heating, and the electrically energized resistors of the selectively energized thermal head array are Used in contact with or near the recording layer. A suitable thermal print head is eg the Fujitsu T
hermal Head (FTP-040 MCS001), TDK Thermal Head F41
5 HH7-1089 and Rohm Thermal Head KE 2008-F3.

The image signal for adjusting the current in the micro-resistor of the thermal printing head may be coupled, for example, from an optoelectronic scanning device or, optionally, with a digital image scanning stage to meet the particular needs of processing the image information. It is obtained directly from a good intermediate storage means, for example a magnetic disk or tape or an optical disk storage medium.

When used in thermographic recordings scanned with a thermal printing head, the recording material is not suitable for the reproduction of images with a considerably higher number of gray levels required for continuous tonal reproduction. Let's do it.

According to EP-A 622 217 relating to a method of forming an image using a direct thermal imaging element, continuous toning is achieved by heating the thermal recording element with a thermal head having a plurality of heating elements. A reproduction is obtained, which is the duty cycle, which displays the ratio of activation time to total line time, with the following formula: P < P _max = 3.3 W / mm ² + (9.5 W / mm ² × Δ) [formula , P _max is the maximum value of the average power density P (expressed in W / mm ² ) diffused by the heating element during the linear time over the heating element]. The activation is performed line by line.

Direct thermal imaging can be used for the production of both transparent and reflective type prints. In the hardcopy field, recording materials on white opaque bases are widely used in inspection techniques operated with light boxes.

While the present invention is described below in connection with its preferred embodiments, it will be understood that the invention is not intended to be limited to that embodiment. On the contrary, the intention is to cover all modifications, alterations, and equivalents included within the spirit and scope of the invention as defined by the appended claims.

The invention is illustrated below by means of examples of the invention and comparative examples. Percentages and ratios given in these examples are by weight unless otherwise stated.

[0068]

【Example】

Examples 1-2 of the Invention and Comparative Examples 1-7-Coating of Thermal Sensitive Element A doctoring coating composition containing butanone as solvent and the following components on a subbed polyethylene terephthalate support having a thickness of 175 μm. After coating with a blade and drying at 50 ° C for 1 hour,
Silver behenate 4.74 g / m ² Polyvinyl butyral (Butvar ^™ B79 from Monsant) 18.92 g / m ² Silicone oil (Baysilone ^™ from Bayer AG) 0.043 g / m ² Benzo [e] [1, 3] Oxazine-2,4-dione, toning agent 0.260 g / m ² 7- (ethylcarbonato) -benzo [e] [1,3] oxazine 0.133 g / m ² -2,4-dione, Toning agent (see formula II below) Butyl 3,4-dihydroxybenzoate, reducing agent 1.118 g / m ² tetrachlorophthalic anhydride 0.151 g / m ² pimelic acid 0.495 g / m ²

[0069]

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A layer containing was obtained.

Coating of the heat-sensitive element with a surface protective layer The heat-sensitive element was coated with various aqueous compositions having the following basic composition, expressed as a weight percentage of the components present next: 2.5% polyvinyl. Alcohol (Wacker Ch
Mowiviol ^™ WX 48 12) from emie, U converted to acid form by passage through a 0.09% ion exchange column
ltravon ^TM W (dispersant from Ciba Geigy), 0.11%
Talc (type P3 from Nippon Talc), 1.2% colloidal silica (Levasil ^™ VP AC from Bayer AG)
4055) Tetramethyl orthosilicate hydrolyzed in the presence of 2.1% methanesulphonic acid and the lubricant in the concentrations given in weight percent in the table below.

The pH of the coating composition was adjusted to a pH of 4 by adding 1N nitric acid. The lubricants in these compositions, which are insoluble in water, were dispersed in a ball mill, optionally using a dispersant. 85 this composition
coated to a wet layer thickness of μm and then dried at 40 ° C. for 15 minutes and 45 ° C. and 70
Cure at 7% relative humidity for 7 days.

Printing and Evaluation After curing, each is printed with different electrical energy per dot and the printing direction using a commercial AGFA DRYSTAR ^™ 2000 (thermal head) printer with a maximum electrical input energy per dot of 63 mW. Of the thermal head with an image consisting of 11 blocks printing a strip 2 mm wide and 2 cm long on either side with a non-printed strip 2 mm wide and 18 cm long orthogonal to the printing direction. Formed across the width. The resulting printability distinguished between these non-printed and printed strips laterally adjacent to these 2 mm widths, ie 2 mm wide and 2 cm long on either side of the 2 mm wide and 18 cm long non-printed strips. Whether or not the printed strips were faithfully reproduced was used as a measure of the image quality obtained. In the case of a 2 mm wide extremely non-homogeneous movement printed on the printed strip, non-uniform movement along the thermal head will produce on either side of the long non-printed strip that is not faithfully reproduced. .

The prints were visually evaluated on a scale of 5 to 0 according to the following criteria: 5, very poor: 2 mm wide and 18 cm long with a clear eye on either side of each unprinted strip. Additional dark white lines visible 4, bad: additional white lines clearly visible at a distance of >> 20 cm on either side of each non-printed strip of width 2 mm and length 18 cm 3, normal: Additional white lines clearly visible at a distance of 20 cm on either side of each non-printed piece of width 2 mm and length of 18 cm 2, good: each non-printed piece of width 2 mm and length of 18 cm. Additional white lines clearly visible at a distance << 20 cm on either side of the strip 1, very good: weakly visible on each non-printed strip of 2 mm width and 18 cm length Additional white line , It is excellent: no white lines appear in additional eye.

Dynamic coefficient of friction is measured by modifying the AGFA DRYSTAR ^™ 2000 (thermal head) printer by adding a strain gauge so that the lateral strain generated by the recording material in contact with the thermal head during the printing process can be measured. did. Using the electrical signal generated by a strain gauge coupled with the thermal head at a load of 330 g / cm of the thermal head and a transfer rate of 4.5 mm / s, then using the scale curve generated by applying the weight to the strain gauge. Then, the absolute dynamic friction coefficient was converted. Over the entire width of a thermal head consisting of 11 blocks, each printed with different energy per dot, and each of which is 2 mm wide in the printing direction and 18 cm long transverse to the printing direction. 2 on either side of it so that there are non-printed pieces
The dynamic coefficient of friction was measured by printing the image with a width of mm and a length of 18 cm. The dynamic coefficient of friction varies with print density. As shown in FIG. 1, the maximum and minimum values were measured as a function of time (sec) from the strain gauge response (volt) printout (= print position). These values, along with the ratio of maximum to minimum, are shown below in Table 1 for Comparative Examples 1-7 and Table 2 for Examples 1-2 of the invention.

Table 1: Comparative Solid Lubricant Liquid Lubricant Dynamic Friction Coefficient Image Example Code Density [%] Code Density [%] Max Min Max / Min Quality 1 SL01 0.18--0.504 0.222 2.27 3 2 SL01 0.36-- 0.437 0.195 2.24 3 3 PSL01 0.09--0.437 0.168 2.60 5 4--LL04 0.18>0.638> 0.444-5 5--LL04 0.36>0.638> 0.444-5 6--PLL01 0.18 0.538 0.256 2.10 4 7 SL01 0.2 LL04 0.1 0.327 0.192 1.70 5 These comparative examples teach that the recording materials showed a dynamic coefficient of friction greater than 0.3 and poor image quality even with varying concentrations of solid or liquid lubricant in the surface layer. Furthermore, the surface of the material with the high concentration of liquid lubricant incorporated in the protective layer was greasy, as in Comparative Examples 2 and 5. Comparative Example 7 teaches that the combination of solid and liquid lubricants as disclosed in WO94 / 11199 also showed a dynamic coefficient of friction greater than 0.3 and very poor image quality. .

Table 2: Solid lubricant of the present invention Liquid lubricant Dynamic friction coefficient Image Example code Density [%] Code density [%] Max Min Max / Min quality 1 SL11 0.18 PLL01 0.09 0.269 0.168 1.60 2 2 PSL01 0.18 PLL01 0.09 0.249 0.175 1.42 1 Examples 1 and 2 of the present invention are both 1 in this case.
Having a melting point below 50 ° C. and at least one of them
0.3 by using a combination of solid and liquid lubricants whose species are phosphoric acid derivatives in the surface layer of recording materials
It teaches that a reduction in the dynamic coefficient of friction below and a reduction in the ratio of the minimum to maximum dynamic coefficient of friction below 1.9 resulted in a significant improvement in image quality.

Examples 3 to 22 of the Invention The recording materials of Examples 3 to 22 of the invention are the same as Examples 1 to 2 of the invention except that an additional solid lubricant was added in the protective layer. Was prepared as described above.

Printing and evaluation were performed as described for Examples 1-2 of the invention, and the results are summarized in Table 3 below.

[0080]

[Table 1]

Examples 3 to 22 of the present invention use a combination of two solids and one liquid lubricant, in this case all having a melting point below 150 ° C. and at least one of which is phosphoric acid. Reduction in dynamic friction coefficient below 0.3 and minimum versus maximum motion below 1.9 by using a combination of solid and liquid lubricants which are phosphoric acid derivatives in the surface layer of recording materials It teaches that a reduction in the ratio of dynamic friction coefficients resulted in a significant improvement in image quality.

Examples 23-26 of the Invention The recording materials of Examples 23-26 of the invention were prepared according to Examples 1-2 of the invention, except that an additional liquid lubricant was added in the protective layer. Was prepared as described above.

Printing and evaluations were performed as described for Examples 1-2 of the invention and the results are summarized in Table 4 below.

[0084]

[Table 2]

Examples 23-26 of the present invention use a combination of two solid and one liquid lubricants, all of which in this case have a melting point below 150 ° C. and at least one of which is phosphoric acid. Reduction in dynamic friction coefficient below 0.3 and minimum versus maximum motion below 1.9 by using a combination of solid and liquid lubricants which are phosphoric acid derivatives in the surface layer of recording materials It teaches that a reduction in the ratio of dynamic friction coefficients resulted in a significant improvement in image quality.

While the preferred embodiments of the invention have been described in detail, those skilled in the art do not depart from the scope of the invention as defined in the claims and the main features and preferred embodiments section. It will be clear that as many modifications as possible can be made.

The main features and aspects of the present invention are as follows.

1. (I) A heat source for the outermost layer of a recording material comprising on a support at least one heat-sensitive element comprising a substantially light-insensitive silver salt and a reducing agent therefor in thermal working relationship therewith. And (ii) imagewise applying heat from the heat source to the recording material while maintaining mutual contact in relative motion between the recording material and the heat source, and (ii)
i) A thermal imaging method comprising the step of separating the recording material from the heat source, wherein the dynamic coefficient of friction during the contact between the outermost layer of the recording material and the heat source is 0.3
A method having a smaller maximum value.

2. The thermal imaging method of claim 1 wherein the ratio of the maximum dynamic friction coefficient to the minimum dynamic friction coefficient is less than 1.9.

3. The image forming method by heat according to 1 or 2 above, wherein the heat source is a thin film thermal head.

4. The thermal imaging method of any of the preceding paragraphs wherein the outermost layer is the outermost layer of the heat sensitive element.

[0092] 5. The thermal imaging method of any of the preceding paragraphs wherein the outermost layer is a protective layer applied to the heat sensitive element.

6. The thermal imaging method of any of the preceding paragraphs wherein the outermost layer comprises a hydrophilic binder.

7. A thermal imaging method according to any of the preceding paragraphs wherein the outermost layers are cross-linked.

8. A thermal imaging method according to any of the preceding paragraphs wherein said outermost layer comprises a matting agent.

9. The thermal imaging method of any of the preceding paragraphs wherein the outermost layer comprises at least one lubricant.

10. 9. The thermal imaging method according to 9 above, wherein the lubricant is selected from the group consisting of silicone derivatives, polyolefins, fatty acid derivatives, fatty alcohol derivatives and phosphoric acid derivatives.

11. The method for forming an image by heat according to any one of the above items, wherein the substantially non-photosensitive silver salt is a substantially non-photosensitive organic silver salt.

[Brief description of drawings]

FIG. 1 is a printout of the strain gauge response (volts) as a function of printing time (seconds) (= printing with 11 blocks each printed with different electrical energy per dot). (Position) is a graph showing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Paul Jiyansen Belgian Bee 2640 Maltsel Septestrat 27 Agfuer-Gevert Namurose Fuennaught Shyup (72) Inventor Johann Rokiyuhuye Belgian B2640 Moltsel・ In Septestrat 27 ・ Aghua-Gevert Namurose ・ Fennaught Shyat (72) Inventor Balth Holsten Belgium B 2640 Maltsel ・ Septestrate 27 ・ Aghua-Gevert ・ Namrose ・ Fennaught Shyat

Claims (1)

[Claims] 1. A recording material comprising at least one heat-sensitive element on a support comprising (i) a substantially light-insensitive silver salt and a reducing agent therefor in thermal working relationship therewith. Contacting the outer layer with a heat source, (ii) applying heat from the heat source to the recording material while maintaining mutual contact with relative motion between the recording material and the heat source, and (iii) A thermal imaging method comprising the step of separating a recording material from the heat source, wherein the coefficient of dynamic friction during contact between the outermost layer of the recording material and the heat source is 0.3. A method having a smaller maximum value.